| We are facing unreliable energy supply, and environmental problems caused by fossil fuels become more and more serious. Therefore, we have to turn to clean and renewable energy in order to realize sustainable development. Solar energy has advantages of clean, extensive distribution and abundant reserves, promising for clean electricity. Fully printable mesoscopic solar cells can be fabricated from low cost materials by printing technique, having advantages of low cost, ease farication and high efficiency. Fully printable mesoscopic solar cells are featured with "TiO2/spacer layer/carbon (abbreviated as TSC)" simple structure and having potential to be commercialized, including monolithic dye-sensitized solar cells and mesoscopic perovskite solar cells during development. Dye-sensitized solar cells based on N719 dye had reached power conversion efficiency (PCE) of 7.73%. Perovskite, presented by CH3NH3PbI3, has excellent physical properties, which makes this semiconductor material be very suitable as light harvesting material in solar cells. Now, perovskite solar cells have reached PCE of over 22%.Spacer affects carrier transporting and light harvesting abitlity in fully printable mesoscopic solar cells, having important role in obtaining highly efficient devices. Perovskite, which grows in the pores of TSC films, is used as light harvesting material and simultaneously hole transporting materials. Therefore, crystal quality of perovskite in TSC films has direct effect on light harvesting and carrier transporting ability. Besides, light soaking stability is one of important prequisites for commercialization and remains a lonstanding issue. In this study, parameters of spacer and perovskite crystal growth will be discussed, and factors affecting light soaking stability of mesoscopic perovskite solar cells will be studied. The main conclusions are the followings:(1) Designing spacer with high reflectivity. Sub-micrometer cavity was used as scattering centers. On one hand this spacer could enhance the ability of reflectivity, and on the other hand the spacer ensured sufficient porosity for transporting electrolyte. By coating spacer nanoparticles with SiO2 acidic oxide to eliminate dye adsorption, spacer possessed significantly improved visible light reflectivity even after immersing in dye solution. The PCE of monolithic dye-sensitized solar cells was improved from 3.95% to 4.61% under simulated AM 1.5 one sun illumination.(2) Systematically investigating the main parameters of spacer affecting the performance of mesoscopic perovskite solar cells. Particle size affects quantum size effect and determines perovskite grain size and grain boundary density. So there was an optimal range for particle size. The experiment showed that, for zirconia,10 nm-60 nm was an optimal range. Spacer layer thickness mainly affects the insulating property and hole transporting distance. For 20 nm zirconia,1 ?m was an optimal thickness. The weight ratio (the powder to ethyl cellulose) of 1:0.5 was the best in the spacer paste.(3) Synthesizing highly dispersed nanoparticles and formulating spacer paste with the prepared nanoparticles to obtain spacer with ultra flat and uniform surface. The results showed that the flat and crack-free spacer could make the contact between the carbon layer and the perovskite layer grown in the spacer smoother and tighter compared to conventional spacer. This improvement was crucial to effectively separate titania from carbon, and for device to uniformly collect carriers in large scale. After optimizing parameters of spacer, with mixed cationic perovskite (NH3(CH2)4COOH)x(CH3NH3)1-xPbI3 as both the light absorbing materials and hole transporting materials, PCE of mesoscopic perovskite solar cells was improved to 12.5% from 10.2% in average, and reached 13.8% in one champion device under simulated AM1.5 one sun illumination.(4) Systematically investigating the main factors affecting CH3NH3PbI3 perovskite crystal growth in the TSC mesoporous films, including precursor solution temperature, substrate temperature, and crystallization routes. At last, TSC films almost fully filled with CH3NH3PbI3 perovskite was obtained, leading to PCE of 13.14% under simulated AM 1.5 one sun illumination.(5) Effects of perovskite pore filling in the TSC films and additives in precursor on light stability of mesoscopic perovskite solar cells were studied. It was found that light stability of device in the air can be enhanced through improving perovskite pore filling in the TSC films. For CH3NH3PbI3, half-life of device was prolonged to over 6 hours from less than one hour. In addition, additives in precursor could significantly improve light stability of solar cells. The additives worked through improving perovskite pore filling in the TSC films, and also making the perovskite grain much more tightly. The as-prepared device made water molecules hard to enter the the crystal structure of CH3NH3PbI3, and kept the chemical bonds of CH3NH3PbI3 stable. PCE of device with 5-AVACl additive was maintained almost unchanged after being exposed continuously in standard simulated AM 1.5G for 40 hours. For another additive, p-AEBACl, light soaking stability was improved but inferior to device with 5-AVACl additive. These differences were analysed and dicussed through XRD and high-resolution SEM. |
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